the last page but one

  1. Open the last but one page of the book.
  2. Open the last page but one of the book.
  3. Open the page, the last but one of the book.
  4. Open the book, turn the last page but on.
    Please mark which are correct.
    If any one is found wrong, guide me to correct.
    Thanks.

1 is correct.
2 is understandable but not as fluent.
3 is incorrect.
4 Open the book, turn to the last but one page.